The ability of a cell to reproduce by cell division is one of the most fundamental processes of all living matter. Abnormalities of these processes are often involved in the growth of transformed cells. Therefore, a thorough understanding of the events involved in normal cell division is crucial to understanding transformed cell growth. To this end several groups have identified a cell division control protein kinase, p34cdc2, that is a crucial component of normal mitosis. Removal of this protein kinase activity has recently been shown to lead to a block in mitosis. However, this system is complex and the proteins that activate this kinase, as well as those that are acted upon by this kinase activity, remain unidentified. We have identified a new protein kinase that is highly related (68% homology) to the p34cdc2 kinase. This new kinase is 394 amino acids in size, is apparently regulated by phosphorylation and Ca2+ - calmodulin, and is localized to the cytoplasm and nucleus. Expression of the corresponding mRNA is regulated during the cell cycle, peaking during G(1)-and S-phase. Elevated expression of this CDC-related kinase in eukaryotic cells leads to an apparent block of the cell cycle at the late telophase and early G(1) boundary. We propose to examine, at a molecular and biochemical level, the nature of this CDC-related kinase and its role in cell cycle control. This will be accomplished by examining its regulation during the cell cycle. Careful analysis of steady-state mRNA and protein levels, kinase activity, phosphorylation state, and protein-protein interactions as a function of cell cycle will be performed using cDNA clones and antibodies for this new CDC-related kinase.We will also examine transcriptional and post-transcriptional regulation of the CDC-related mRNA as a function of cell cycle. Hybridization data indicates that sequence-related transcripts exist in humans and mice. These sequences will be isolated and sequenced to determine whether a larger gene family exists. Finally, the structure/function of this new CDC-related kinase will be examined by deletion and site-specific mutagenesis, as well as expression in eukaryotic cells. These studies will ultimately define the role of this CDC-related kinase in both normal and transformed cell growth, and are essential for understanding the molecular basis of cell division control.